Electric motor rotor with permanent magnets

ABSTRACT

An electric motor rotor with permanent magnets, the rotor including magnets ( 20 ) seated against a cylindrical lateral surface ( 11 ) of the core ( 10 ) of the rotor and a pair of annular caps ( 40 ), each cap being seated and affixed to an adjacent end face ( 12 ) of the core ( 10 ), the annular caps ( 40 ) limiting axial displacements of the magnets and defining, for both directions of circumferential displacement, stops for this displacement for each magnet ( 20 ), the confronting lateral edges ( 21 ) of a pair of consecutive magnets ( 20 ) being positioned by the annular caps ( 40 ), in order to define a previously established minimum circumferential distance.

This is a national phase application under 35 U.S.C. §371 ofInternational Application No. PCT/BR98/00085, filed Oct. 22, 1998, andclaims the benefit under 35 U.S.C. §119 Brazilian Pat. Application No.PI9705306-6, filed Oct. 24, 1997.

FIELD OF THE INVENTION

The present invention refers to a construction for a brushless electricmotor rotor comprising a metallic core, which carries, on its lateralsurface, circumferentially disposed magnets.

BACKGROUND OF THE INVENTION

In the known constructions for a brushless electric motor rotor, thepermanent magnets, usually in the form of arcuated plates, are retainedon a cylindrical core, usually made of iron, which may be laminated ormassive and which is mounted around the motor shaft.

In these rotors, the magnets are provided in housings defined bylongitudinal openings inside the metallic core or kept seated on thecylindrical lateral surface of the core through different fixationmeans, which are designed to impart to the mechanical structure thenecessary resistance to centrifugal forces and to the motor operation.

In the rotor construction in which the magnets are affixed to thecylindrical lateral surface, one of the assembly problems results fromthe need to maintain the longitudinal axis of the magnets parallel tothe longitudinal axis of the core. This positioning is usually obtainedby providing external radial saliences incorporated to the surface ofthe rotor core or by equipments for carrying out the assembly of theunit during the manufacturing process.

These techniques have the inconvenience of making difficult thepositioning of the magnets on the rotor surface during manufacture,which positioning should be angularly correct and provide a determinedangular distance between the magnets. This difficulty is due to thedegree of longitudinal freedom existing during assembly.

The positioning of the magnets on the rotor surface by means of externalradial saliences of the core causes an assembly difficulty, whichresides on the fact that the magnets are supported on only one of saidsaliences, since, during the operation of the motor or also during themounting process of said rotor, the different thermal expansion of boththe magnets and the core may generate high mechanical stressesconcentrated on the magnets at the supporting region, in case themagnets are simultaneously supported on two opposite saliences. Thesestresses may cause failures caused by magnet breakage, as they areformed of ceramic material. In certain cases, even the support on onlyone salience can be critical.

After the formation of the rotor, with the magnets correctly positionedaround the core, the rotor has to be positioned and mounted around themotor shaft, when positioning means are required to align the rotorduring its assembly phase around the motor shaft. These positioningmeans also position the rotor for the posterior magnetization of themagnets, which has to be effected in a predetermined position of saidmagnets in relation to the motor structure. This positioning function isusually provided by bores, which are made in the magnetic core of therotor and which reduce the amount of active material of said core,impairing the efficiecy of the motors or limiting the minimum size thatthe rotors may have, without the bores impairing relevantly theperformance of said motor.

Another deficiency of the prior art is the high manufacturing cost ofthe rotors, as a function of the high investments required, when usuallyautomatic positioning equipments are used.

DISCLOSURE OF THE INVENTION

Thus, it is an objective of the present invention to provide an electricmotor rotor with permanent magnets, which allows the magnets to beprecisely seated onto the external surface of the rotor core, withoutrequiring constructive changes in the core or precision equipments.

Another objective of the present invention is to provide an electricmotor rotor of the type having permanent magnets and which allows tosimplify the automatic mounting process of the rotor.

These and other objectives are attained by an electric motor rotor withpermanent magnets, said rotor including a core having a cylindricallateral surface, against which are seated magnets having oppositelateral edges, said rotor comprising a pair of annular caps, each capbeing seated and affixed onto an adjacent end face of the core, saidannular caps limiting the axial displacements of the magnets anddefining, for both directions of circumferential displacement, stops forthis displacement for each magnet, the confronting lateral edges of apair of consecutive magnets being positioned by said annular caps, inorder to define a previously established minimum circumferentialdistance.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described below, with reference to the attacheddrawings, in which:

FIG. 1 illustrates, schematically and in a longitudinal sectional view,a rotor with the annular caps of the present invention disposedaccording to a mounting embodiment;

FIG. 2 shows, in a perspective view, a rotor provided with the annularcaps of the present invention;

FIG. 3 illustrates an upper plan view of the annular cap of FIG. 1;

FIG. 4 shows a lateral view of the annular cap of FIG. 3;

FIG. 5 shows a perspective view of the annular cap;

FIG. 6 shows, schematically, a plan view of a rotor provided with a pairof annular caps acting on the magnets of said rotor;

FIG. 7 shows, schematically and in a partially plan view anotherembodiment of the annular caps of the sent invention; and

FIG. 8 illustrates, schematically, a detail of a peripheral portion ofan annular cap, according to another embodiment of the presentinvention, using, for example the cap illustrated in FIG. 7.

BEST MODE OF CARRYING OUT THE INVENTION

The present invention refers to an electric motor rotor of the type withpermanent magnets and having a core 10 to be affixed around an extensionof the motor shaft S and in whose cylindrical lateral surface 11 areseated magnets 20, usually in the form of arcuated magnetic plates, saidmagnets 20 being retained against the core 10, for example by gluing orby actuation of a tubular cylindrical cap 30, so that each of theirrespective lateral edges 21 be spaced from a confronting lateral edge 21of an adjacent magnet by a previously determined minimum distance.

According to the present invention, the electric motor rotor furthercomprises a pair of annular caps 40 in a material with a permeabilitysubstantially inferior to that of the core 10, which is preferably madeof a non-magnetic material, each cap being affixed to the core 10 andseated on an adjacent end annular face 12 of the latter, in order tocover or not the adjacent end 21 of the magnets 20, said annular caps 40limiting the axial displacement of the magnets and defining, for bothdirections of circumferential displacement, stops for this displacementfor each magnet 20, the confronting lateral edges 21 of a pair ofconsecutive magnets 20 being limited by said annular caps 40 so that,during the positioning of the magnets 20 on the rotor core, said lateraledges 21 do not surpass the previously established minimumcircumferential distance for each two consecutive magnets 20.

Each annular cap 40 carries, from a peripheral edge 41 thereof,circumferential displacement limiting stops 42, which are, for instance,incorporated to the annular cap 40 and which will be described below,each stop limiting the circumferential displacement of a respectivemagnet 20 in one direction of circumferential displacement, each magnet20 having its circumferential displacement, in both directions, limitedby at least two circumferential displacement limiting stops 42, each onebeing mounted to one of the annular caps 40, adjacent to an end portionof a lateral edge 21, said circumferential displacement limiting stops42 being adjacent to end portions of diagonally opposite lateral edges21.

In another embodiment of the present invention, at least one of theannular caps 40 comprises circumferential displacement limiting stops 42which limit both directions of circumferential displacement of arespective magnet 20.

In one solution of the present invention, the circumferentialdisplacement limiting stops 42 are provided according to a samecicumferential alignment internal to the circumferential alignment ofthe external face of the magnets 20.

The fixation of the annular cap 40 to the core 10 is carried outappropriately, for example through a retaining element 50, which islongitudinally extended across the core 10 and which affixes the annularcaps 40 to each other and to the core 10.

Though not illustrated, other forms of retaining the annular caps 40 tothe core 10 are possible within the inventive concept presented (such asrivets, screws, etc.,) which may or may not extend throughout the axiallength of the rotor core.

In the illustrated embodiments, each annular cap 40 incorporates, in asingle piece, a peripheral annular flange 43, defined, for example on aplane which is parallel in relation to the plane of the annular cap 40,said peripheral annular flange 43 carrying the circumferentialdisplacement limiting stops 42, for example in the form of axial earsincorporated to the annular cap 40 and projecting from the plane of theperipheral annular flange 43 of the latter and which are angularlyspaced from each other, each defining a circumferential stop, actingagainst an end portion of a lateral edge 21 of a respective magnet 20,upon mounting the magnets around the rotor core. The peripheral annularflange may be further defined parallel or coplanar in relation to theplane of the annular cap 40.

The circumferential displacement limiting stops 42 should have adetermined flexibility, sufficient to allow the deformation thereof, forexample resulting from thermal expansion of the magnet for which itactuates as a circumferential displacement limiting means. An eventualdeformation of said stops 42 avoids high stresses on the magnets 20 andthe consequent damages caused to said magnets.

The annular caps are attached to the rotor, so that theircircumferential displacement limiting stops 42 assure that theconfronting lateral edges 21 of a consecutive pair of magnets 20 bepositioned at a determined previously established minimum distancebetween said magnets when mounted around the rotor core.

According to the embodiment illustrated in FIGS. 1-6, the minimumcircumferential distance is achieved by the joint actuation of bothannular caps 40. In this case, the annular caps 40 should be positionedone in relation to the other, so that their respective circumferentialdisplacement limiting stops 42 be circumferentially offset by a valuewhich positions to the magnets 20 with the minimum circumferentialdistance therebetween. In the embodiments illustrated in FIGS. 7 and 8,the circumferential displacement limiting stops 42 are provided in eachannular cap 40 in order to define the minimum circumferential distancebetween each two adjacent magnets 20.

In the embodiment illustrated in FIG. 8, the circumferentialdisplacement limiting stops 42 are radially and angularly spaced fromeach other, in order to avoid mutual contact in any deformationcondition of said magnets 20.

The circumferential displacement limiting stops 42 have their lengthdimensioned, considering the possible dimensional variations (andmargins of error) in the length of said magnets. For the construction ofFIGS. 7 and 8, the distance between each two adjacent circumferentialdisplacement limiting stops 42 related to a respective magnet is definedtaking into account the variations of circumferential extension (andmargins of error) of said magnets 20.

The circumferential displacement limiting stops 42 of the presentsolution are designed to guarantee, upon assembly of the magnets 20 tothe rotor core, a desired relative positioning between said magnets,without however necessarily acting against said magnets 20 during thisassembly condition or even after obtaining the retaining condition ofsaid magnets to the rotor core.

In the construction of FIG. 8, the annular caps 40 are attached to therotor, so that their respective circumferential displacement limitingstops 42, acting on the same lateral edge portion 21 of each magnet 20be axially aligned to each other. However, in order to obtain thepositioning with the desired minimum distance, it is sufficient to haveonly one of the annular caps with adjacent circumferential displacementlimiting stops 42, each limiting the positioning of a respective magnet20.

According to the illustration in FIG. 1, the annular caps 40 are affixedto the core 10 so that each magnet 20 mounted to the core 10 has a pairof circumferential displacement limiting stops 42, each acting againstan adjacent end portion of one of the diagonally opposite lateral edges21.

In the illustrated embodiments, the circumferential displacementlimiting stops 42 are also equally spaced from each other, as a functionof their actuation in relation to the magnets 20. However, thedistribution of the circumferential displacement limiting stops 42throughout the peripheral annular flange 43 of each annular cap 40 maypresent variable spacings, defined as a function of the actuation ofsaid circumferential displacement limiting stops 42 on each magnet 20.

The level difference between the plane of the annular cap 40 and itsperipheral annular flange 43 allows the use of magnets having an axiallength which may be larger or smaller than that of the rotor core.

The attachment of at least one of the annular caps 40 to the core 10determines the circumferential positioning for retaining each magnet 20to said core 10. The assembly of the annular cap 40 adjacently to thelower end face of the core 10 further determines an axial retention ofsaid magnets 20 in relation to the core 10. This retention results fromeach magnet 20 being seated against an inner face of the peripheralannular flange 43 of the annular cap 40 located at the bottom of thecore 10.

In the embodiment in which the circumferential displacement limitingstops 42 are in the form of axial ears, the latter may be formed withthe same material of the corresponding cap 40 and incorporated in asingle piece thereto (by stamping, casting, injection, etc.) andproduced by one of the processes of folding, stamping, bending, etc., ormay be affixed to the respective cap 40 by an adequate process, such asriveting, welding, gluing or mechanical interference. The axial ears 42attachable to the annular cap 40 may be obtained from a differentmaterial than that which forms the annular cap 40.

The joint actuation of the pair of annular caps 40 in relation to thecore 10 determines a circumferential and longitudinal alignment of themagnets 20 seated on the rotor core.

According to the present invention, each annular cap 40 is furtherprovided with positioning means 44 in the form of bores or portionswhich are upwardly drawn from the surface of the annular cap 40, saidpositioning means 44 allowing the angular positioning of the rotor uponassembly of the magnets (or, eventually, during the formation orplacement of the cap around said magnets), said positioning means 44avoiding the need for providing bores in the magnetic core of the rotorand circumferentially locking the rotor in relation to the shaft S,during the assembly in any of the mounting positions of the magnets orcap, mainly when the latter is coiled.

With this construction, the assembly with the correct circumferentialand longitudinal alignments of the magnets 20 in relation to the core 10is achieved in a simple way, with no need for using sophisticatedequipments, or removing material from the core 10, since no bores aremade in the latter, making the motor more efficient and/or more compact.The circumferential displacement limiting stops 42 further avoid theoccurrence of concentrations of mechanical stresses of thermal origin,which usually lead to breakage of the magnetic material.

While constructions were illustrated (FIGS. 6 to 8), in which themagnets 20 are tightly positioned in relation to each of the annularcaps 40, particularly in relation to the respective annular flange 43and axial ears 42, it should be understood that said constructions allowan assembly having axial and circumferential gaps between the magnets 20and annular flange 43 and axial ears 42 of each annular cap 40.

Though not illustrated, the annular cap 40 of the present invention maypresent the circumferential displacement limiting stops 42 in the formof radial projections, each provided with a respective axial extensionorthogonal to the plane of the annular cap, said radial projectionsacting in the circumferential locking of at least one adjacent magnet20.

What is claimed is:
 1. An electric motor rotor with permanent magnets,said rotor including a core (10) having a cylindrical lateral surface,against which are seated magnets (20) having opposite lateral edges(21), characterized in that it comprises a pair of annular caps (40),each cap being seated and affixed to an adjacent end face (12) of thecore (10), said annular caps (40) limiting axial displacements of themagnets and defining, for both directions of circumferentialdisplacement, stops for the circumferential displacement for each magnet(20), the opposing lateral edges (21) of a pair of consecutive magnets(20) being positioned by said annular caps (40), in order to define apreviously established minimum circumferential distance, each annularcap (40) comprising positioning means (42), each one limiting thecircumferential displacement of a respective magnet (20) in onedirection of circumferential displacement, each magnet (20) having itscircumferential displacement limited in both directions by twocircumferential displacement limiting stops (42), each said limitingstop provided in one of the annular caps (40), said circumferentialdisplacement limiting stops (42) which act on the same magnet (20) beingseated against diagonally opposite end portions of lateral edges (21) ofsaid magnet (20).
 2. An electric rotor, as in claim 1, characterized inthat the circumferential displacement limiting stops (42), which areprovided in both annular caps (40) and which act on the same magnet(20), are each seated against the end portion of an adjacent lateraledge (21) of a magnet (20).
 3. An electric motor rotor, as in claim 2,characterized in that the adjacent circumferential displacement limitingstops (42) of an annular cap (40), each limiting the circumferentialdisplacement of a magnet (20) in one direction of displacement, arespaced from each other by a distance corresponding to the minimumcircumferential spacing to be maintained between the magnets (20).
 4. Anelectric motor rotor, as in claim 1, characterized in that each annularcap (40) incorporates, in a single piece, a peripheral annular flange(43) which carries the circumferential displacement limiting stops (42).5. An electric motor rotor, as in claim 4, characterized in that thecircumferential displacement limiting stops (42) are defined by axialears attached to the peripheral annular flange (43).
 6. An electricmotor rotor, as in claim 5, characterized in that each axial ear isincorporated, in a single piece, to the respective annular cap (40). 7.An electric motor rotor, as in claim 6, characterized in that each axialear is produced by one of the processes of stamping, folding and bendingan extension of the peripheral annular flange (43) of the respectiveannular cap (40).
 8. An electric motor rotor, as in claim 6,characterized in that the axial ears are attached by one of theprocesses of riveting, welding, gluing and mechanical interference. 9.An electric motor rotor, as in claim 1, characterized in that eachannular cap (40) is obtained by one of the processes of stamping,injection and casting.
 10. An electric motor rotor, as in claim 1,characterized in that the annular caps (40) and the circumferentialdisplacement limiting stops (42) are provided in a material with apermeability substantially lower than that of the core (10).
 11. Anelectric motor rotor, as in claim 1, characterized in that it includes,from an external face of each annular cap (40), positioning means (44)having at least one of the functions of angular positioning the rotor inrelation to the motor shaft during the assembly of the magnets (20),formation of a cap around said magnets (20) and circumferentiallylocking the rotor in relation to the motor shaft (S), in any of theassembly conditions of said magnets (20) and said caps.
 12. An electricmotor rotor, as in claim 1, characterized in that each annular cap (40)incorporating the respective annular flange (43) and axial ears (42) isobtained by one of the processes of stamping, injection and casting,said annular flange (43) and said axial ears (42) being obtained, in thestamping operation, by one of the processes of folding and bending theannular cap (40).